Method of forming rifling in a gun barrel by chemical milling

ABSTRACT

A method of forming rifling, including that of a gain twist configuration, by the chemical milling process in the bore of a barrel which may include a liner of a refractory material. A template rod made of an acid resistant material which is radially compressible and which has a diameter slightly greater than that of the bore is pressed thereinto so that liquid tight contact is made between the surfaces of the rod and bore. A plurality of spiral channels and uninterrupted areas are formed in the rod to image the desired rifling configuration. A closed circulatory system delivers fluid acid to one end of the channels, and the rifling grooves formed thereby, and after passing therethrough returns the acid to the pump for recirculation. A pressure gage between the pump and barrel may be used in lieu of an elapsed time for chemical reaction to indicate when the rifling grooves are formed to the desired depth.

United States Patent 11 1 Di Benedetto et a1.

METHOD OF FORMING RIFLING IN A GUN BARREL BY CHEMICAL MILLING Inventors: Josepe D. Di Benedetto, Moline, 111.; Walter M. Kisner, Davenport, Iowa Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.

Filed; Aug. 23, 1971 Appl. No.: 173,996

us. (:1 156/16, 156/19, 156/345 1m. c1 C23g 3/04 Field of Search 156/16, 6, 19, 25, 156/345 References Cited UNITED STATES PATENTS 6/1959 Hays 156/19 12/1959 lversen 156/25 7/1969 Vandersteen 156/8 3,751,313 Aug. 7, 1973 Primary Examiner-lacob H. Steinberg Attprmeu-Harry M. Saragovitz, Edward J. Kelly et a1.

[57] ABSTRACT in the rod to image the desired rifling configuration. A

closed circulatory system delivers fluid acid to one end of the channels, and the rifling grooves formed thereby, and after passing therethrough returns the acid to the pump for recirculation. A pressure gage between the pump and barrel may be used in lieu of an elapsed time for chemical reaction to indicate when the rifling grooves are formed to the desired depth.

4 Claims, 4 Drawing Figures PAIENIED m WV E mm M mmm.m WESQ.0.W M m D A hm W PE u mm W Fig AC;

BY u Kim 1 METHOD OF FORMING RIFLING IN A GUN BARREL BY CHEMICAL MILLING BACKGROUND OF THE INVENTION This invention relates to methods of forming rifling in gun barrel bores and pertains more particularly to a method of forming rifling in gun barrel bores by chemical milling.

The methods used almost entirely today in the manufacture of rifled gun barrels employ broaching or swaging techniques which are excellent for production type operation where the metal being worked is steel although the machines and tooling required are relatively expensive and the techniques require skilled operators. It is impractical, however, to utilize these techniques in production type operations to form gain twist rifling in barrels having a bore surface of refractory material because of the machining characteristics thereof.

It is therefore a principal object of this invention to provide a method of forming rifling with a gain twist in a barrel having a bore surface of a refractory material, which is practical for production operations.

It is a further object of this invention to provide a me thod of forming rifling in a gun barrel bore, be it constant or gain twist, or of a multilayer or monolithic construction or otherwise composed of metallic material, which does not require the expensive machines and tooling of the broaching and swaging techniques and which does not require skilled operators to perform the method.

It is another object of this invention to provide a method of forming rifling in a gun barrel tube in which maintenance costs respective to cooling are minimal.

It is still another object of this invention to provide a method of forming rifling in a gun barrel bore in which the method of gaging the depth of the rifling grooves is incorporated in the forming method.

These objects are achieved by a novel method of utilizing the chemical milling process in the technique of forming rifling in a gun barrel tube. In this method the rifling is formed by use of a selected acid especially suited to corrosively attack the material in which the rifling is to be formed and which is controlled in its attack by a template of rod configuration pressed with a tight fit into the barrel bore. The template rod is provided with channels and uninterrupted surfaces therebetween in theimage of the desired rifling to be formed in the barrel bore. The rod is fabricated from an acid resistant material which has a limited radial compressibility, such as teflon, and has a diameter slightly greater than that of the bore so that when the rod is pressed thereinto the uninterrupted surfaces have liquid tight contact with the bore surface.

The fluid acid is pumped at a predetermined pressure to one end of the barrel and after passing through the channels in the rod the acid is clarified, and the gases vented, and then is .returned to the pump for recirculation. A pressure gage is located in the circulating system between the pump and barrel to indicate the pressure at which the acid is applied to the barrel. As the rifling grooves are formed the resistance to the flow of the acid from the pump is decreased and the amount of this decrease indicates the depth to which the grooves are then formed.

Further objects and advantages of the invention will become apparent from the following specification, and

the accompanying drawing which is for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Shown in the drawings is an apparatus for performing one method of forming rifling 12 by chemical milling in the surface bore 14 of a barrel 16 having a liner 17 of a refractory material, which rifling comprises a plurality of spiral grooves 18 and lands 20 located therebetween. This method uses apparatus comprising a liquid circulating system 22, as shown in FIG. 1, for delivering to and from barrel 16, as hereinafter described, a fluid in the form of an acid selected as best suited for eroding the metal from which liner 17 is fabricated. The acid is supplied to system 22 by means of a conduit 23, and a shut-off valve 24 from source 25. 7

System 22 comprises a pair of connectors 26 which fit, respectively, over the opposite ends of barrel 16 to make liquid sealed contact with the outside surface thereof, as shown in FIG. 4. One of the connectors 26 is connected by conduit 28 to a pump 30 which supplies the acid under pressure to that end of barrel l6'and which is adjustable to a specific pressure output. A pressure gage 32 is located in system 22 between pump 30 and barrel 16 to indicate the pressure at which the acid is supplied thereto.

The other one of the connectors 26 is connected by conduit 29 to a suitable type clarifier 34 which serves to separate any foreign, solid matter from the acid and to vent from system 22 those gases which are generated by the chemical milling process. Clarifier 34 is connected to pump 30 by conduit 31. A three-way valve 42- is located in system 22 forwardly of barrel 16 to provide means for stopping the passage of the acid thereto and opening that end of the barrel to'the passageof water or suitable acid neutralizer thereto. A similar valve 44 is introduced into system 22 after the barrel to provide means for either directing the acid to clarifier 34 or the flushing water or neutralizer from the system.

Rifling 12 is formed in the surface of bore 14 through the controlled application of the acid thereto by a template rod 36 having a plurality of spiral channels 38 formed in the outside thereof in the image of grooves 18 to be formed in the surface of bore 14 and uninterrupted portions 40 of the outer surface of the rod, between the channels, which are in the image of lands 20. Rod 36 has the same length as bore 14 and is formed from a material which is acid resistant and has slight de gree of radial compressibility, such as Teflon. The diameter of rod 36 is slightly greater than that of bore 14 so that when the rod is force fitted thereinto uninterrupted portions 40 make liquid tight contact with the surface of the bore and so protects the contacted surface from the erosive action of the acid when passing through channels 38.

Thus, with pump 30 adjusted to a specific pressure output, acid is supplied thereby to one end of barrel l6 and then is forced along channels 38, and grooves 18 after their formation is initiated, and out the opposite ends thereof for delivery by conduit 29 to clarifier 34 where any solid matter and the gases generated by the erosion of the bore surface is separated from the acid before being returned to the pump for recirculation. Passage of the acid through channels 38 permits erosive action of the acid on the areas along bore 14 which are not protected by uninterrupted portions 40 thereby forming grooves 18 to the desired depth.

The amount of metal removed from the surface of bore 14 along channels 38 is determinable by the pressure indicated by gage 32 because, as the metal is removed, the resistance to the flow of the acid through barrel 16 is correspondingly decreased, as shown by comparing FIG. 2 to FIG. 3. When the pressure indicated on gage 32 reaches the amount predetermined as being the pressure of the acid supplied to barrel 16 when grooves 18 are formed to the correct depth, pump 30 is stopped. Valve 42 is then turned to stop the flow of the acid to barrel l6 and permit the flow of water or an acid neutralizer thereto and valve 44 is turned to permit the discharge of the water or neutralizer after passing through the barrel. When grooves 18 are thoroughly washed, barrel 16 is uncoupled from connectors 26 and rod 36 is removed from bore 14 ready to be used in another barrel because no wear is made upon the rod by this process.

It is also possible to predetermine a fixed time for sufficient chemical reaction to occur for forming grooves 18 to the desired depth and thereby eliminate the necessity for gages. It is also possible to form rifling 12 by photoengraving with bore 12 being selectively masked by photographic techniques.

We wish it to be understood that we do not desire to be limited to the' exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

We claim:

1. The method of forming a rifling by the chemical milling process in the surface of a bore in a gun barrel, said rifling having a plurality of spiral grooves and lands formed therebetween, said method including the steps of masking said surface of said barrel bore by forming in a rod of acid resistant material and having a limited radial compressibility, a length similar to that of said barrel and a diameter slightly greater than that of said bore a plurality of spiral channels conforming to the contours of said grooves and uninterrupted portions of the surface of said rod to effect an image of said rifling, pressing said rod into said bore with a force fit thereby making liquid tight contact between said uninterrupted portions and said surface of said bore, and passing a fluid acid through said channels until the corrosive attack thereof against the surface of said bore at said channels forms said rifling to the desired depth.

2. The invention as defined in claim 1 and including the steps of installing said barrel in a closed, liquid circulating system, pumping said acid to one end of said bore for passage through said channels, and removing any foreign solid matter and the gases generated by the chemical milling process from said acid before being returned to said pump for recirculation.

3. The invention as defined in claim 2 and including the steps of adjusting said pump to a specific pressure output, gaging the pressure of said acid as supplied to said barrel, and comparing the pressure gaged to that determined as being the pressure of the acid to the barrel according to the adjusted pressure when said grooves are formed to the desired depth.

4. The invention as defined in claim 2 and including the step of stopping the erosive action of said acid on said bore surface after a period of time predetermined as being sufficient for the formation of said grooves to the desired depth. 

2. The invention as defined in claim 1 and including the steps of installing said barrel in a closed, liquid circulating system, pumping said acid to one end of said bore for passage through said channels, and removing any foreign solid matter and the gases generated by the chemical milling process from said acid before being returned to said pump for recirculation.
 3. The invention as defined in claim 2 and including the steps of adjusting said pump to a specific pressure output, gaging the pressure of said acid as supplied to said barrel, and comparing the pressure gaged to that determined as being the pressure of the acid to the barrel according to the adjusted pressure when said grooves are formed to the desired depth.
 4. The invention as defined in claim 2 and including the step of stopping the erosive Action of said acid on said bore surface after a period of time predetermined as being sufficient for the formation of said grooves to the desired depth. 